In the field of absorbent articles including disposable diapers and sanitary napkins, it is a practice widely adopted to bond an elastic member in its stretched state to a sheet material and allow the elastic member to contract thereby to make gathers (an extensible portion with a large number of folds) of the sheet.
JP-A-2001-11769 (reference-1) discloses an elastically extensible sheet having a flat sheet material accordion-folded to make a large number of folds and elastic members bonded to the top of a plurality of the folds.
Japanese Utility Model 2518953 (reference-2) discloses a disposable diaper having an elastically extensible portion having a sheet material of nonwoven fabric folded back into two layers and an elastic member sandwiched between the two layers. The sheet material is joined to itself along linear joints extending in a direction perpendicular to the extending direction of the elastic member, and the elastic member is bonded to the sheet material at the joints.